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APSY 2216
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Thomson
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Lecture 7

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Counseling, Developmental, and Educational Psychology

APSY 2216

Thomson

Spring

Description

ANNOUNCEMENTS
● Research Plan Drafts are due Friday on Canvas
○ First of two times you’ll turn in this assignment - just a draft
● You can sign up for Wednesday office hours on Canvas or just drop by
● Exam in two weeks: Wednesday, February 22
● So far we have…
○ Identified a research problem
○ Defined a question and hypothesis
○ Reviewed the literature to find out what is known about the problem
● We still need to…
○ Determine the best method for studying what is not known
■ Sample participants - Who?
■ Instruments - What?
■ Procedure - When? Where? How?
■ Consider validity and reliability
○ Analyze and interpret data obtained through the method
SAMPLING
● Sample - any group on which information is obtained
○ Should be representative of the population based on key characteristics (ex: gender, ethnicity, etc.)
○ Sampling - the process of selecting a number of individuals from a population, preferably in a way
such that the individuals are representative of the larger group from which they were selected
○ Non-random sampling - not every member of the entire population has an equal chance of being
selected → can be biased
■ Systematic sampling - obtained by selecting every nth name in the population
● Disadvantage: people may be arranged on a list in a particular order, if the whole
population is available anyway, why not conduct random sampling?
● Least often done
■ Purposive sampling - selected based on personal judgment of the population, choosing
based on specific characteristics that you would not know about the larger population
● Ex: selecting 100 students from each group: high GPA, middle GPA, low GPA
● Used pretty often
■ Convenience sampling - obtained based on availability of potential participants ● Ex: putting up posters in coffee shops
● Least ideal
● Theoretically, it produces a non-representative sample and should be avoided, but
practically, one of the most commonly used sampling methods
○ Random sampling - method of selecting subjects from population by chance so that bias is less
likely
■ Simple random sampling - take a list of every single person in your population and give
them each an ID number, then use a random number table to pick subjects
● Advantages: if the random sample is large enough, it is likely to be representative of
a population
● Disadvantages: technical difficulty (you need a list of every member of the
population - impossible with a large population), subject to error, especially for
smaller samples, no guarantee that all subgroups of interest are going to be
adequately represented
■ Stratified random sampling - certain subgroups (strata) are preselected to reflect their
proportion in the population → first divide population into strata (ex: SES and gender), then
select a random sample from each stratum to preserve the proportion as it exists in the
whole population
● Ex: 30% of population are high SES boys → select 30% of high SES boys for sample
● Advantages: increases likelihood of representation, ensures that key characteristics
are included
● Disadvantages: only makes sense if we suspect that different strata may vary in
their behaviors, technical difficulty (still need list of every member of population)
■ Cluster random sampling - random selection of groups instead of individuals → the more
groups selected, the more likely the sample is to be representative
● Ex: select certain schools, certain classes, etc.
● Disadvantage: selected groups may not be representative
■ Two stage random sampling - first cluster sample, then simple random sampling
● Ex: randomly select zip codes (clusters) and then randomly select people within the
zip code

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